Kołacz Jakub, Konya Andrew, Selinger Robin L B, Wei Qi-Huo
Advanced Materials and Liquid Crystal Institute at Kent State University, Kent, OH 44240, USA.
Soft Matter. 2020 Feb 26;16(8):1989-1995. doi: 10.1039/c9sm02424g.
Thermophoresis, or the directional motion of colloidal particles in liquids driven by a temperature gradient, is of both fundamental interest and practical use. In this work we explore the thermophoresis of colloids suspended in nematic liquid crystals (LCs). We observe that the motion of these colloids is fundamentally different from that in isotropic systems as a result of elastic distortions in the director fields caused by the colloidal inclusions. In the case of a sufficiently large local temperature and gradient, the elastic energy drives negative thermophoresis of immersed particles, which has a strongly nonlinear dependence on temperature. We develop a theory that incorporates elastic energy minimization into the traditional thermophoretic formulation and demonstrated a good agreement with experimental observations. We also examine the temperature dependence of the effective viscosity of the colloids and highlight the large magnitude of the Soret coefficient (|ST| > 5000), which results from the inherent enhancement in thermophoresis due to elastophoretic considerations and suppression of Brownian diffusion in LC media.
热泳现象，即由温度梯度驱动的液体中胶体粒子的定向运动，既具有基础研究价值，又具有实际应用价值。在这项工作中，我们探索了悬浮在向列型液晶（LC）中的胶体的热泳现象。我们观察到，由于胶体夹杂物引起的指向矢场中的弹性畸变，这些胶体的运动与各向同性系统中的运动有根本不同。在局部温度和梯度足够大的情况下，弹性能驱动浸入粒子的负热泳，这对温度有强烈的非线性依赖。我们发展了一种理论，将弹性能最小化纳入传统的热泳公式，并与实验观察结果取得了良好的一致性。我们还研究了胶体有效粘度的温度依赖性，并强调了索雷特系数的巨大数值（|ST| > 5000），这是由于弹性电泳考虑导致的热泳固有增强以及LC介质中布朗扩散的抑制所致。
